This research exploits the cardiac ganglion of crabs and lobsters as a model in which to seek basic knowledge of endogenous neuronal properties, their biophysical bases, the mechanisms by which they are modified and controlled by synaptic interactions, both electronically and chemically mediated, mechanisms of integration, and the mode of action on an integrating neural system of a peptide neurohormone. The ganglion exhibits spontaneity, stable rhythmicity and burst impulse firing. With 9 neurons, it is the smallest neural system that can be isolated functionally intact which exhibits major features of central nervous system functioning. Electrophysiological techniques employing several intracellular and extracellular electrodes simultaneously will be used. They permit monitoring of all impulse traffic, evaluation of synaptic interactions and recording of endogenously generated potential changes such as pacemaker (PMP) and burst forming or 'driver' potentials (DP). The characterization of DPs, recently found to persist in the absence of other responses in tetrodotoxin, will be refined and extended. Functional isolation and biophysical characterization of DP's with voltage clamping techniques will be undertaken. Functional and electronmicroscopical (EM) localization of the sites of chemical and electronic synaptic interaction will be studied. The cardioactive peptide hormone(s) of crab pericardial organs will be separated and their mode of action in enhancing burst rate, duration and coordination analyzed. Knowledge gained from study of this model system may be expected to contribute and have general relevance to basic understanding of CNS functioning.